1. Field of the Invention
The present invention relates to a device for a feeding magnetic head, and more specifically to a device for feeding a magnetic head in a magnetic recording/reproducing apparatus employing a disc-like recording medium.
2. Description of the Prior Art
Conventional devices (positioners) for determining positions of the head employed in the magnetic recording/reproducing apparatus of this kind can be divided into those which determine the positions relying upon a closed loop system and those which determine the positions relying upon an open loop system.
A device relying upon the closed loop system consists of a linear motor which is energized by a servo circuit, a moving plate to which an end of a head-supporting spring is secured so that the head is permitted to move, and the like. Namely, this device is based upon a so-called data servo system in which a tracking position is recorded beforehand in the data-recording track on the disc, and when the data is to be reproduced, the signal is detected to so control the linear motor relying upon the control circuit that the head moves up to a predetermined position to reproduce the signals at an optimum position. There also exists a servo-surface servo system, according to which a special head is provided at a place (back surface of the disc is often used) which is different from the data track to record position signals (servo signals) only, and servo signals are reproduced and processed through a servo circuit to move the linear motor, such that the head interlocked thereto is moved to an optimum position.
With the closed loop servo systems employing linear motors, the head can be positioned maintaining increased precision, but increased manufacturing cost is required to realize a servo system which consists of servo circuits and linear motors.
According to a conventional device for positioning head based upon the open loop system, on the other hand, use is made of a pulse motor 3 as a drive source as shown in FIG. 1, and pulses are produced by a control circuit 1 in a number necessary for moving the head to a desired position. Currents are supplied to each of the phases of the pulse motor from a pulse motor drive circuit 2, or rotational direction of the pulse motor is changed, in order to turn the pulse motor in a required direction by a required amount. As the pulse motor 3 rotates, a belt 4 is wound around the central position of the shaft of the motor. Namely, the belt 4 of which the two ends are fastened to a moving plate is pulled toward either side depending upon the turn of the shaft, and one end of the moving plate 5 is pulled by the belt toward either side (toward the side of the disc or toward the opposite side), so that the head 6 on the disc 7 moves.
According to the open loop system in which position signals on the disc are not fed back to determine the position, the positioning precision is determined by the combination of precision in stop angle of the pulse motor, gap of the mechanism, dimensional change in the elements and parts caused by the temperature, and the like. Therefore, the open loop system has poorer positioning precision than the closed loop positioning system. Despite this fact, the open loop system has been widely used owing to its low manufacturing cost and compact size.